The production of methanol and methanol derivatives is a well-known process in the chemical production industry. There are published methods using solid catalyst, heterogenous slurry catalyst and homogenous liquid catalyst. Over 95 percent of methanol produced today involves the use of a Fischer-Tropsch (“F-T”) type solid catalyst in a reactor vessel of a particular style including: a packed bed catalyst arrangement, tubular catalyst arrangement or micronized solid particles of F-T catalyst in a slurry form carried in an organic or inorganic solvent.
This novel invention takes particular advantage of a highly efficient homogenous liquid methanol producing catalyst for producing methanol directly from syngas containing carbon monoxide, hydrogen, nitrogen, carbon dioxide and trace amount of other gases including methane. More particularly this invention describes reacting syngas in the presence of a homogenous liquid catalyst inside a novel bubble column reactor.
Methanol is a valuable chemical intermediate and fuel product. The growing demand for energy products in a safe liquid form makes the production of methanol a valuable energy resource. Methanol production processes use syngas containing mainly hydrogen and carbon monoxide as a gaseous feedstock to produce methanol product.
Syngas is a common name given to a gas mixture that contains varying amounts of hydrogen and carbon monoxide. Examples of production methods include steam reforming of natural gas or liquid hydrocarbons to produce hydrogen, the gasification of coal, biomass, and in some types of waste-to-energy gasification facilities. The name comes from their use as intermediates in creating synthetic natural gas and for producing ammonia or methanol.
Gasification is a thermochemical pyrolytic process that converts carbonaceous materials, such as coal, petroleum, biofuel, or biomass, into carbon monoxide and hydrogen by reacting the raw material, such as house waste, or compost at high temperatures with a controlled amount of oxygen and/or steam. The resulting gas mixture is called syngas.
The advantage of gasification is that using the syngas is potentially more efficient than direct combustion of the original fuel because it can be combusted at higher temperatures or even used in fuel cells, so that the thermodynamic upper limit to the efficiency defined by Carnot's rule is higher or not applicable. Syngas may be burned directly in internal combustion engines, used to produce methanol and hydrogen, or converted via the Fischer-Tropsch process into synthetic fuel. Gasification can also begin with materials that are not otherwise useful fuels, such as biomass or organic waste. In addition, the high-temperature combustion refines out corrosive ash elements such as chloride and potassium, allowing clean gas production from otherwise problematic fuels.
Gasification relies on chemical processes at elevated temperatures >700° C. (>1290° F.), which distinguishes it from biological processes such as anaerobic digestion that produce biogas.
Depending upon the specific method of producing syngas the ratio of hydrogen to carbon monoxide will vary. The reaction to produce methanol generally requires a hydrogen to carbon monoxide ratio of at least 2 to 1. The reference to a hydrogen to carbon monoxide ratio describes how the syngas contains a minimum of 2 moles of hydrogen for every mole of carbon monoxide. To achieve a minimum of a 2 to 1 ratio of hydrogen to carbon monoxide syngas may be conditioned through the use of a water gas shift reaction.
The water-gas shift reaction is a chemical reaction in which carbon monoxide reacts with water vapor to form carbon dioxide and hydrogen:CO+H2O→CO2+H2
The water-gas shift reaction is an important reaction step in the production of syngas for use in methanol production. It is also often used in conjunction with steam reforming of methane or other hydrocarbons, for the production of high purity hydrogen for use in ammonia synthesis.
Syngas produced from wood or biomass gasification or pyrolysis possesses a typical hydrogen to carbon monoxide molar ratio of 1 to 1. Therefore, syngas conditioning to increase the molar concentration of hydrogen is necessary. In this case a water gas shift reaction is used to increase the hydrogen concentration.
Syngas production is commonly found using hydrocarbon or natural gas as the primary carbon source. There are many sources of natural gas located in isolated regions which are far from pipeline access. Natural gas co-produced with crude oil is typically partially consumed locally to produce heat for process equipment, electricity for local needs and in some cases can be re-injected with a gas compressor into the oil bearing formation to maintain geological formation pressures. More typically it is simply burned in a thermal flare allowing the oil production company the ability to produce a greater volume of crude oil.
Methanol can be produced from any carbon-based source. These would include: natural gas, coal, municipal wastes, landfill gas, wood wastes, aquatic and subaquatic biomass. Methanol is primarily produced by steam-reforming natural gas to create a syngas which is fed into a reactor vessel in the presence of a nickel catalyst to produce water vapor and methanol. A distillation step is used to remove water from the finished methanol.
Methanol is considered a portable source of energy. About 34 percent of the input gas (energy) is lost in its synthesis so its production away from markets requires very cheap natural gas supply to be viable for large volume production systems. Transport costs impact heavily on its viability. There are many reasons why methanol is an important key to a syngas-based fuels and chemical industry. First, methanol is synthesized in over 99% or greater selectivity, in sharp contrast to the wide array of other hydrocarbon products, from methane to waxes, obtained in the Fischer-Tropsch (F-T) reaction. Second, the weight retention of syngas (2H2: 1CO) as a feedstock for methanol is 100%. Syngas is a costly raw material for the production of hydrocarbons obtained in the F-T reaction where oxygen is eliminated as water or CO2. Third, methanol furnishes selective pathways to a number of important chemicals, including formaldehyde and the widely used two carbon oxygenated chemicals. This route to fuels and to two carbon chemicals from methanol is more attractive than the direct synthesis from syngas.
For over many years, new increases in methanol production capacity have been driven by countries with large oil and/or natural gas reserves, building methanol facilities as a way to transport and monetize “stranded gas” resources. Little new capacity has been based on byproduct growth. Generally, systematic rationalization has followed at a pace similar to expansion, particularly in the high-cost natural gas-based areas like North America and Europe.
Globally methanol production capacity stands at between 40 and 50 million metric tons per year (approximately 14 to 15 billion gallons). The operating methanol production plants in the United States have greatly reduced capacity given the much higher cost of natural gas used in the production of methanol. Total demand for methanol in the United States is over 8 million metric tons (2.6 billion gallons), with United States based production satisfying only approximately 5 percent of this demand, with imports mainly from Trinidad, Chile, Venezuela, Equatorial Guinea and Canada making up the remaining supply. Generally, one metric ton of methanol equals 333 gallons.
In the United States and other parts of the world, smaller and more regional resources for syngas production are available. In 2013 the National Renewable Energy Laboratory (“NREL”) reported that it estimated 7.9 million metric tons a year of methane generation potential for selected biogas sources in the United States, including: wastewater, landfills, animal manure, IIC organic waste. This is equal to about 420 billion cubic feet or 431 trillion British thermal units (“BTU”). According to a 2013 report by the Energy Information Association, this amount of energy produced from biogas could displace about 5% of current natural gas consumption in the electric power sector and 56% of the natural gas consumption in the transportation sector. The availability of low cost or stranded natural gas in the U.S. is growing. Many areas of development lack pipeline infrastructure to transport the natural gas to a market. Those isolated sources of natural gas that do have pipeline infrastructure available earn sub market value for their product due to the high cost of pipeline transmission to a consumption point.
In the case of biomass to methanol the concept of transporting biomass to a centralized, large scale methanol production plant is uneconomical. If biomass is transported a distance of 100 miles or greater the cost of transportation raises the cost of the biomass to uneconomical cost levels for the conversion into methanol.
In both the case of stranded or isolated natural gas, as with biomass resources, there exists a real need for a small scale (micro-plant) methanol production process capable of using the regional natural gas, biomass or other carbon based resources available. Once produced into a methanol product the regional market can take advantage of the regionally produced methanol product as opposed to sourcing the product from a distant, many times foreign source for the product. The novel invention provides a small, modular, micro-plant option for energy companies.
In contrast, today all commercial methanol process plants operating are constructed on a very large scale, high volume production basis. A typical methanol process plant today is constructed with capacities ranging from 1,000 to 5,000 metric tons per day (333,000 up to 1,665,000 gallons per day). The micro-plant methanol production reactor is constructed with a capacity ranging from 0.5 to 30 tons per day (166 to 10,000 gallons per day). The current F-T commercial process systems available today are unable to reach these low capacities of production economically.
Various methods have been developed for the production of methanol from gas mixtures containing carbon monoxide, hydrogen and carbon dioxide, among these are:
U.S. Pat. No. 6,881,759 discloses a process for methanol production in a liquid phase reactor from a synthesis gas comprising of hydrogen, carbon dioxide, and carbon monoxide. The liquid phase reactor contains a solid catalyst suspended in methanol. In this invention the methanol acts both as a product and as a suspension medium for the catalyst. A part of the methanol in the reactor is withdrawn from the reactor in the form of methanol product.
U.S. Pat. No. 5,179,129 discloses a process to produce methanol from syngas comprising of hydrogen, carbon monoxide and carbon dioxide in a two-stage liquid phase reactor system. Each reactor is operated at optimum temperature range to maximize methanol productivity, and once through product conversion of 9.1 moles methanol per 100 moles of syngas can be achieved.
U.S. Pat. No. 4,766,154 discloses a process for the production of methanol from a syngas feed containing carbon monoxide, carbon dioxide and hydrogen. The process described is a combination of two liquid phase methanol reactors into a staging process, such that each reactor is operated to a favor of a particular reaction mechanism. The first reactor is controlled to favor the hydrogenation of carbon monoxide, and the second reactor is controlled to favor the hydrogenation of carbon dioxide.
U.S. Pat. No. 4,628,066 discloses a process for increasing the capacity of a gas phase synthesis loop for the production of methanol from a syngas feed. The syngas feed is initially passed to a liquid phase methanol reactor to convert a portion of the syngas to methanol or methanol and higher aliphatic alcohols. The mixture is subsequently cooled to condense and recover the methanol and/or higher alcohols. The unreacted syngas is passed to a gas phase synthesis loop for further conversion and recovery of methanol.
U.S. Pat. No. 4,567,204 discloses a process for the production of methanol in a liquid phase methanol reactor by entraining a methanol forming catalyst in an inert liquid and contacting the entrained catalyst with a synthesis gas comprising of carbon monoxide and hydrogen.
U.S. Pat. No. 4,346,179 discloses a process for producing methanol and its higher homologs from a synthesis gas containing essentially carbon dioxide, carbon monoxide, and hydrogen. A synthesis gas is treated in a first catalytic reaction zone at 230-350° C. The effluent from the first catalytic reaction zone is cooled and condensed and as a gas fraction is separated from the liquid condensate. The gas fraction is subsequently treated at 240-300° C. in a second catalytic reaction zone to produce a liquid methanol fraction. The liquid methanol fraction is subsequently admixed with the liquid condensate to form a gasoline constituent product.
U.S. Pat. No. 4,235,799 discloses a process for producing methanol by passing a mixture of hydrogen and one or more carbon oxides into contact with at least two beds of catalyst arranged in series. The catalyst beds are operated at increasing temperature levels in the direction of flow of the mixture. The mixture is subsequently cooled by indirect heat exchange and passed into contact with at least further bed of catalyst.
U.S. Pat. No. 4,031,123 discloses a similar method for preparing methanol with the improvement that paraffinics and cycloparaffinnics are used as the inert hydrocarbon liquid which the catalyst bed is in contact.
U.S. Pat. No. 3,888,896 discloses a process for producing methanol from carbon monoxide and hydrogen by saturating an inert organic liquid medium, such as pseudocumene, with carbon monoxide and hydrogen and contacting the saturated liquid medium with methanol forming catalyst such as those containing zinc and chromium.
U.S. Pat. No. 1,868,096 discloses a process for producing methanol by passing a reaction gas mixture under the request conditions of temperature and pressure initially over one or more catalyst masses composed of zinc oxide or zinc oxide and chromium oxide and subsequently passing said mixture over one or more methanol catalysts sensitive to sulfur poisoning such as catalysts comprising of copper, manganese or compounds of copper or manganese. The reaction gases are passed successively through a number of reactor vessels arranged in series as an open system.
Canadian Pat. No. 1,157,053 discloses a liquid phase methanol synthesis process wherein methanol is produced by contacting a synthesis gas comprising hydrogen and carbon monoxide with a catalyst in presence of an inert liquid. The catalyst in contact with the inert liquid is in the form of particles of a size less than about 125 microns.
U.S. Pat. No. 1,302,011 discloses a invention relates to a method of producing methyl alcohol from alkyl formates by treating an alkyl formate with hydrogen in the presence of an appropriate catalyzer to decompose the formate whereby methyl alcohol and the alcohol derived from the alkyl contained in the alkyl formate in question is formed.
Existing processes using 2 to 1 syngas to produce methanol operate at far greater pressure and temperatures. The inventors are unaware of any existing methanol production process system which use low pressure syngas and low reaction temperatures using a homogenous type catalyst to produce methanol in commerce.